Method and System for Controlling Computer Tomography Imaging

ABSTRACT

A method, a device, a system and a computer program are for controlling limited-area computer tomography imaging. The method includes determining location data of a first imaging object when the first imaging object is positioned in an imaging area, determining reference location data related to the first imaging object and adjusting the imaging area based on the location data of the first imaging object and said reference location data for imaging a second imaging object. The first and the second imaging object can be located at a distance determined by the reference location data from each other or symmetrically in relation to the reference location data.

The invention relates to a method, a device and a system for controllingX-ray imaging. The present invention particularly relates to controllinglimited-area computer tomography imaging performed in the teeth and jawarea.

TECHNICAL BACKGROUND

The imaging of the teeth and jaw area employs the so-called limited-areacomputer tomography devices, an example of which are cone-beam computedtomography imaging devices (CBCT). The device transilluminates thepatient's skull by a beam in order to collect volume element data at adesired point in the skull and a three-dimensional image isreconstructed of the skull point in question based on the data produced.The devices are used in the teeth and jaw area speciality in diagnosingand planning treatment e.g. in procedures related to surgery,implantology and oral pathology.

An X-ray apparatus employed in limited-area computer tomography imagingtypically comprises a rotating arm attached at one end of a supportingframe, at opposite ends of which are attached a device generating X-raysand a device detecting X-rays. Exposure to X-rays is performed byrotating the rotating arm, whereby the movements of the rotating arm andthus also the device generating X-rays and the device detecting X-raysare synchronised such that an image of an area of desired size e.g. ofthe patient's tooth or jaw joint is provided to the device detectingX-rays. Typically, the rotating arm is rotated around its stationaryrotation axis. The device detecting X-rays is e.g. a CCD (chargedcoupled device) or a CMOS sensor which registers radiation havingpenetrated the object being imaged.

The diameter of the area being imaged is typically only a part of thediameter of the whole skull or jaw area. In X-ray imaging, it isimportant to position the imaging area of the object to be imagedprecisely in a correct location in relation to the imaging apparatus.For imaging, it is also important that the object remains stationary.The positioning of the imaging area—and simultaneously the positioningof the patient to be imaged—is started by choosing and locating theobject to be imaged, which can be assisted by using e.g. pointers andindicators implemented by lights or e.g. another X-ray image taken ofthe object.

For instance, from specification U.S. Pat. No. 6,118,842 is known anX-ray apparatus applicable for limited-area computer tomography imaging,where between the device generating X-rays and the device detectingX-rays is located an object positioning means for positioning the objectto be imaged in the imaging area. In relation to their locations, theobject positioning means, the device generating X-rays and the devicedetecting X-rays are relatively adjustable in the anteroposterior,lateral and vertical directions. From specification U.S. Pat. No.6,118,842 is also known an X-ray apparatus for limited-area computertomography imaging, where the location of the object positioning meanspositioned between the device generating X-rays and the device detectingX-rays is adjustable in relation to the frame of the X-ray apparatus inthe anteroposterior, lateral and vertical directions. Then, the imagingarea is located on a straight line according to the rotation axis of therotating arm, around which the device generating X-rays and the devicedetecting X-rays rotate. The precise location of the object positioningmeans in said directions can be adjusted by an adjustment mechanismwhich is installed between the frame of the X-ray apparatus and theobject positioning means. When adjusting the location of the objectpositioning means, it is possible to utilise object positioning datawhich has been obtained from a tomographic image taken earlier of theobject by panoramic imaging. The adjustment of the location of theobject positioning means can also utilise a light beam sent by a lightindicator located on the rotation axis of the rotating arm, whereby theimaging area of the object is precisely in the correct place when thelight beam focuses on the object positioning means or the object beingimaged.

In the above limited-area computer tomography devices according to priorart, the object to be imaged is chosen one by one and the object to beimaged is positioned in the imaging area by the object positioning meansone by one before performing the actual X-ray imaging. Then, a newobject to be imaged is chosen and it is positioned in the imaging areaby the object positioning means, after which the actual X-ray imaging isperformed. The positioning of the imaging area is thus performed as itsown separate measure for each object chosen to be imaged. Each objectbeing imaged is imaged to imaging-specific coordinates determined by thepositioning of the imaging area.

When wishing to use the prior-art apparatus to image e.g. the patient'sboth jaw joints, the first jaw joint to be imaged is first positioned bythe object positioning means in its place in the imaging area, afterwhich it is imaged, and then the second jaw joint to be imaged ispositioned by the object positioning means in its place in the imagingarea, after which it is imaged. In order to be able to image both jawjoints, the patient being imaged has to be positioned twice by theobject positioning means to the imaging area, because both jaw jointsare imaged separately. Each separate positioning of the patient forimaging takes time and consumes human and device resources. Furthermore,when the patient being imaged is positioned twice by the objectpositioning means to the imaging area for imaging the jaw joints, bothjaw joints are imaged in their own coordinates. After this as anadditional step, both images have to be registered in one way or anotherin the same coordinates before being able to make comparisons andmeasurements between the objects having been imaged. When the separatelyshot images are registered in the same coordinates, extra auxiliarymeans are required, the dimensions and geometry of which are known andwhich are visible in both images, or the images must have a common areawhich is visible in both images.

A problem of the above arrangements is also that they do not in any wayconsider the special characteristics related to the location or theresemblances of the object to be imaged. The human body has e.g. severalimageable objects which are located in pairs on both sides of the body.Often, the imaging need relates to both such objects in order to be ableto compare possible differences in the objects. Such objects in thehuman body are e.g. the above-mentioned jaw joints which aresymmetrically located on two sides of the skull. When imaging byprior-art devices, both jaw joints must be positioned in the imagingarea and imaged separately, whereby two positioning periods forpositioning the imaging area are required to image the jaw joints. Thetwo separate positionings of the imaging area also cause the fact thatthe jaw joints are imaged in different coordinates, the registering ofwhich in the same coordinates requires the above-mentioned additionalmeasures. Thus, imaging particularly objects located symmetrically ondifferent sides of the body or the skull is slow and awkward.

SUMMARY

An object of the invention is to eliminate disadvantages related to theprior art. According to an object, the invention aims at simplifying andspeeding the work flow of computer tomography imaging. A particularobject of the invention is to speed up object positioning for computertomography imaging when the objects to be imaged are located e.g.symmetrically on two sides of the human body.

According to an additional object, the invention aims at diversifyingthe possible uses of X-ray image data.

An object of the invention is provided by a method according to claim 1,an object by a device according to the independent device claim, anobject by a system according to the independent system claim, and anobject by a computer program according to the independent computerprogram claim.

An embodiment of the invention relates to the method according to claim1, an embodiment to the device according to the independent deviceclaim, an embodiment to the system according to the independent systemclaim, and an embodiment to the computer program according to theindependent computer program claim.

Other embodiments of the invention are described in the dependentclaims.

In the method according to an embodiment of the invention forcontrolling limited-area computer tomography imaging, location data of afirst imaging object is determined, reference location data related tothe first imaging object is determined, and an imaging area is adjustedbased on the location data of the first imaging object and saidreference location data for imaging a second imaging object belonging tothe object.

The device according to an embodiment of the invention, e.g. a controldevice or a control unit, for controlling limited-area computertomography imaging is arranged to determine location data of a firstimaging object, determine reference location data related to the firstimaging object, and to adjust an imaging area based on the location dataof the first imaging object and said reference location data for imaginga second imaging object belonging to the object.

The system according to an embodiment of the invention for controllinglimited-area computer tomography imaging, which comprises at least e.g.an X-ray imaging device and a control device or unit integrated orotherwise connected to it, is arranged to determine location data of afirst imaging object, determine reference location data related to thefirst imaging object, and to adjust an imaging area based on thelocation data of the first imaging object and said reference locationdata for imaging a second imaging object belonging to the object.

The computer program according to an embodiment of the invention forcontrolling limited-area computer tomography imaging comprises codemeans which is arranged to determine location data of a first imagingobject, determine reference location data related to the first imagingobject, and to adjust an imaging area based on the location data of thefirst imaging object and said reference location data for imaging asecond imaging object belonging to the object.

Terms presented in this document are employed, inter alia, in thefollowing meanings:

An ‘object’ refers to e.g. an entity, e.g. a human body, skull or jawarea, where objects being imaged, e.g. jaw joints, belong to.

An ‘imaging area’ refers to e.g. an area where the imaging object ispositioned or set automatically whereby, when imaging, the imagingobject is positioned in relation to the imaging means as optimally aspossible such that a sharp X-ray image is provided with least possibleX-ray exposure of the imaging object.

‘Location data’ refers to e.g. data which relates to a point in theimaging object having been positioned, to be positioned or automaticallyset in the imaging area from which a limited-area computer tomographicimage is to be taken, from which the image is being taken or from whichthe image has already been taken. Location data is e.g. data presentedin three-dimensional coordinates.

‘Reference location data’ refers to data related to an entity, datarelated to e.g. a human body, skull or jaw area, which can indicate therelative location of the objects being imaged belonging to the entity,e.g. jaw joints, e.g. their symmetrical location on opposite sides ofthe body in relation to each other.

According to an example of the invention for controlling limited-areacomputer tomographic imaging, the location data of a first imagingobject is determined when the first imaging object is positioned in theimaging area.

According to an example of the invention, the reference location datarelated to the first imaging object is determined and the imaging areais adjusted based on the location data of the first imaging object andsaid reference location data for imaging the second imaging objectbelonging to the object, whereby the second imaging object is located ata distance determined by the reference location data from the firstimaging object.

According to an example of the invention, the reference location datarelated to the first imaging object is determined and the imaging areais adjusted based on the location data of the first imaging object andsaid reference location data for imaging the second imaging objectbelonging to the object, whereby the first and the second imaging objectare located symmetrically in relation to the reference location data.

According to an example of the invention, the reference location datarelated to the first imaging object is determined and the imaging areais adjusted based on the location data of the first imaging object andsaid reference location data for imaging the second imaging objectbelonging to the object by limiting the X-ray by a collimator, wherebythe first and the second imaging object are located symmetrically inrelation to the reference location data.

According to an example of the invention, the first and the secondimaging object are imaged in one go during one imaging event.

The method according to the embodiments of the invention speeds up thepositioning of the imaging object for limited-area computer tomographyimaging, whereby it is sufficient for positioning objects to be imagedlocated symmetrically on both sides of the body that one of the objectsbeing imaged is positioned in the imaging area. Then, time spent inpositioning the imaging area decreases considerably when compared to asituation where both objects to be imaged, e.g. both jaw joints, areseparately positioned in the imaging area for imaging.

Furthermore, the method according to the embodiments of the inventionsimplifies the work flow of computer tomography imaging because, withone imaging area positioning, both objects to be imaged, e.g. imagingobjects symmetrically located on both sides of the human body, registercomparably to each other, advantageously in the same coordinates,whereby the imaging objects can be compared to each other withoutadditional measures required for image processing or extra accessoriesby which the images having been imaged in separate coordinates areconfigured to register comparably to each other in the coordinates.

Additionally, the method according to the embodiments of the inventionexpands the possible uses of X-ray image data, because X-ray images ofboth imaging objects are imaged during one imaging event, whereby bothimaging objects are together in common coordinates.

According to the invention, to an X-ray image data file are saved e.g.projection images taken of the object to be imaged in X-ray image dataformat, of which further processing reconstructs three-dimensional X-rayimages, and to the X-ray image data file are saved also completedthree-dimensional X-ray images and sets of cross-sectional images formedof them for possible further processing.

SHORT DESCRIPTION OF FIGURES

Next, advantageous embodiments of the invention will be described inmore detail with reference to the attached drawings, where

FIG. 1 shows by way of an example a flow chart of a method according tothe invention,

FIG. 2 shows by way of an example a diagram of the jaw area and animaging arrangement according to the invention in the jaw area,

FIG. 3 shows by way of an example a diagram of the jaw area and anotherimaging arrangement according to the invention in the jaw area,

FIG. 4 shows by way of an example a flow chart of a device according tothe invention, and

FIG. 5 shows by way of an example a flow chart of a system according tothe invention.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 shows a method according to the invention for controllinglimited-area computer tomography imaging, where in a starting step (notshown in the figure) the user starts a computer and a computer programoperating in it which controls imaging and the imaging apparatus.

In step 101, an imaging object is chosen for imaging, which is typicallya part of an object forming a specific entity e.g. a human body,skeleton, skull, jaw area or other equivalent object. The imaging objectcan be e.g. a jaw joint, a single tooth, a set of teeth or some otherpart of an object forming an entity.

In step 103, a patient is positioned in relation to the imagingapparatus such that limited-area computer tomography imaging of thechosen imaging object can be performed. The imaging object to be imagedis positioned in an imaging area which is located between a devicegenerating X-rays and a device detecting X-rays. The location of theimaging area is determined by the relative mutual location of the devicegenerating X-rays, the device detecting X-rays and the imaging object inrelation to each other, which relative location can be adjusted e.g. inthe anteroposterior, lateral and vertical directions.

According to an embodiment, the imaging object is positioned in theimaging area by an object positioning means such that the objectpositioning means supports e.g. the patient's jaw, neck, forehead, earsor some other equivalent point in the object, whereby the actual imagingobject can be positioned precisely and fixedly in the imaging area forcomputer tomography imaging. The location of the object positioningmeans is adjustable in relation to the device generating X-rays and thedevice detecting X-rays e.g. such that the object positioning means, thedevice generating X-rays and the device detecting X-rays are adjustablysupported on e.g. the frame of the imaging apparatus.

In step 105, location data of the imaging object being imaged isdetermined in the imaging area, when the imaging object has beenpositioned in the imaging area. The location data of the imaging objectin the imaging area is determined by the relative mutual location of thedevice generating X-rays, the device detecting X-rays and the imagingobject or the object positioning means in relation to each other, whenthe imaging object is positioned in the imaging area. The location dataof the imaging object in the imaging area can be determined e.g. basedon the size and/or diameters of the imaging object, whereby the locationdata can be associated with e.g. desired points in the imaging objectand presented e.g. in three-dimensional coordinates. The location dataof the imaging object is proportioned to e.g. the frame of the imagingapparatus or the rotary axis of the supporting arm connecting the devicegenerating X-rays and the device detecting X-rays to each other.

According to an embodiment, the imaging object in the imaging area ispointed by an indicator means and the indicator means indicates thelocation data of the imaging object. Then, the indicator means sensesdata related to location and indicates e.g. on a display data related tolocation, the indicator means being stationary or moving. The datarelated to location sensed by the indicator means is saved in a memoryin the control device. The indicator means can be provided with e.g. alight, laser or equivalent indicator, whereby the indicator can point adesired imaging object or a point of the object the relative location ofwhich in relation to the actual imaging object, e.g. a distance, spacingand/or angle, is known. This way, it is possible e.g. to point thepatient's outer auditory canal by the indicator means to determine thelocation data of the jaw joint in the imaging area, as the jaw joint isvery typically at the same point in relation to the outer auditory canalfor all people. In this case the jaw joint being positioned in theimaging area, when the indicator means is used for pointing the outerauditory canal, the indicator means indicates the location data of thejaw joint in the imaging area.

According to an embodiment, the location data of the imaging object inthe imaging area is determined based on earlier data related to thelocation of the same imaging object received from the memory of thecontrol device. Then, the indicator of the indicator means can be setautomatically to show the location data of the imaging object receivedfrom the memory, whereby e.g. a light indication sent by the indicatormeans intersects the imaging object, e.g. its centre, in the imagingarea. According to an example, the indicator means receives from thememory earlier location data related to the same patient's jaw joint,whereby the indicator of the indicator means sets automatically to showthe location data received of the jaw joint.

According to an embodiment, the location data of the imaging object inthe imaging area is determined based on an earlier image of the sameimaging object taken by limited-area computer tomography imaging,intraoral imaging or panoramic imaging. Specification U.S. Pat. No.6,118,842 describes, inter alia, a dual-purpose imaging apparatus whichfirst takes a panoramic image of the imaging object in the panoramicmode, which is analysed and processed to obtain location data and, afterthat, the same imaging object can be positioned in the imaging area forlimited-area computer tomography imaging based on the location dataobtained.

According to some embodiments of the method, step 105 can precede step103. For instance, the location data of the imaging object is determinedand, after that, the imaging apparatus is directed such that the imagingobject is positioned in the imaging area.

In step 107, the imaging object in the imaging area is imaged by alimited-area computer tomography apparatus the location data of whichhas been determined in accordance with steps 103 and/or 105. When theimaging object is in the imaging area, the device generating X-rays andthe device detecting X-rays rotate around the imaging object beingbetween them in the imaging area, whereby desired projection images ofthe imaging object are taken e.g. on each cycle of 180-360 degrees. Thewhole imaging object in the imaging area can be imaged by a specificnumber of projection images. The projection images are saved e.g. inX-ray image data format to an X-ray image data file for furtherprocessing.

Alternatively in step 107, the imaging object is in the imaging areawhen the imaging area is adjusted by limiting X-rays by at least onedynamic collimator, whereby the device generating X-rays and the devicedetecting X-rays rotate around the imaging object being between them inthe imaging area such that a rotation centre formed by the devicegenerating X-rays and the device detecting X-rays does not move duringimaging between the imaging objects at all. It is also possible toimplement the focusing of the imaging area in a combined way where themore precise imaging area is searched by limiting X-rays by at least onedynamic collimator and by moving the rotation centre between the imagingobject but for a shorter travel than the full distance of the imagingobjects.

In step 109, reference location data related to the location data of theimaging object in the imaging area is determined, when the imagingobject is in the imaging area. According to some embodiments of themethod, step 109 can precede or succeed step 103 or can be performed aspart of step 103.

Reference location data refers to data related to an object, e.g. ahuman body, skull or jaw area, and, on the other hand, it refers to databelonging to the imaging object being imaged belonging to the object,e.g. a jaw joint. According to an embodiment, the reference locationdata describes e.g. a symmetry plane, symmetry axis, centre line orequivalent data of the object on different sides of which the imagingobjects belonging to the object are located symmetrically. For instancein the human body, there are several such imaging objects. Jaw joints,for example, are located symmetrically on two sides of the symmetryplane of the skull or jaw area. According to an embodiment, thereference location data describes e.g. a distance between imagingobjects belonging to the object.

In step 109, reference location data is determined which relates to e.g.the measures or dimensions of the head or skull or some other object.Later, some examples of such measurements will be described. Thereference location data can be determined e.g. based on the head orskull width. Then, the reference location data advantageously determinese.g. a distance between desired imaging objects. Alternatively, thereference location data can be advantageously determined before step103. Then in step 103, the object positioning means supports the objectbeing imaged, e.g. the patient's head, in order to keep it stationary.According to an embodiment, based on the determined reference locationdata, the indicator means as earlier described points at a point wherethe imaging object being imaged should be located in order to be in theimaging area, or a point where a specific part of the object, e.g. thenose or jaw, should be located in order for the imaging object beingimaged to be in the imaging area. By means of the reference locationdata, the indicator means indicates the above-mentioned point e.g. by alight, laser or other equivalent indicator. The indicator meansindicates data related to location e.g. on the display of the indicatormeans. The data related to reference location sensed by the indicatormeans is saved in the memory in the control device.

In step 109, reference location data is determined which relates to e.g.the symmetry plane of the head or skull or some other object.Alternatively, the reference location data can be advantageouslydetermined before step 103. Then in step 103, the object positioningmeans can be directed based on the reference location data. The objectpositioning means can support the object being imaged, e.g. thepatient's head, at a desired point such that it remains stationary.Alternatively, the object positioning means can be directed e.g. suchthat the object positioning means supports the object at the point of aplane determined by its reference location data, e.g. symmetry plane,whereby in relation to the plane determined by the reference locationdata, e.g. symmetry plane, the object is divided symmetrically into twoparts.

In step 111, the location data of the imaging object belonging to theobject and the reference location data related to the imaging objectdetermined in step 109 are proportioned to each other by the controldevice.

According to an embodiment, the reference location data is determined bya visual inspection in step 109. For instance the object being the head(skull), a visual inspection can indicate it being divided symmetricallyinto two parts seen from the front in relation to a plane passing viathe nose and the jaw, whereby the plane representing the referencelocation data is a symmetry plane passing via the nose and the jaw.Respectively, it can be presumed that the jawbones with their teeth andjaw joints is divided symmetrically according to the same planedetermined by the reference location data as the head and the skull. Forexample, each point in the symmetry plane formed by the left and theright jaw joint is at an equal distance from both jaw joints. Accordingto an embodiment, the reference location data is determined by pointingby an indicator means of the above type by a visual inspection e.g. thenose and/or the jaw, whereby the indicator means indicates the referencelocation data. Then, the indicator means senses e.g. data related to thelocation of the nose and/or jaw and indicates data related to locatione.g. on the display of the indicator means. The data related toreference location sensed by the indicator means is saved in the memoryin the control device. The indicator means can be provided with e.g. alight, laser or other equivalent indicator, whereby the indicator canpoint at the desired point in the object. In step 111, theabove-mentioned indicator means pointing the imaging object and theindicator means pointing the reference location data are scaled andcalibrated with each other, whereby the location data sensed anddisplayed by them and saved by the computer are comparable with eachother. The object can be directed according to a plane determined byreference location data e.g. such that the object positioning means,e.g. a jaw, forehead, neck and/or other equivalent support, is set tosupport the object, the head, according to the plane determined by itsreference location data, whereby the object positioning means,advantageously its centre line, supports the head at the point of itssymmetry plane. Alternatively, the object positioning means can supportthe object being imaged, the head, at a desired point such that itremains stationary.

According to an embodiment, the reference location data is determined instep 109 by measuring a dimension of the patient's head, e.g. skullwidth, whereby the reference location data can be determined based onthe dimension measured. Advantageously, said dimension measured or datacalculatable of it is used as the reference location data. Themeasurement of the patient's skull width can be performed in many knownways, e.g. by means of lighting measurement. The measurement of thepatient's skull width can also be performed in a way described in thedocument EP1161122. According to an example, the object positioningmeans comprises at least two support elements which are adjustable tosupport the patient's head from different sides, e.g. at the point of orabove the ears, whereby a distance between the support elementsadjustable against each other is denoted by W1. When the supportelements are adjusted such that they both are fast in the skull at thewidest point of the head, a distance between them i.e. the skull widthis denoted by W2. Furthermore, the object positioning means can comprisee.g. a support element supporting the forehead, whereby the supportelements form a ‘headgear’ setting closely on the head, where thesupport elements are adjustable in relation to each other. Respectively,it is possible to measure a skull height H by adjusting the supportelements below the jaw and on the plane of the crown or a skull depth Dby adjusting the support elements on the plane of the forehead and theback of the head. Advantageously, said two opposite support elements areconnected with sensors which produce an electric signal comparable tothe distance W1, H or D and equivalently the width W2, height or depthof the patient's skull to the computer in a way described e.g. inspecification EP1161122. For instance, electric signals of differentsizes produced by the sensors equal the values of different distancesW1. From the measured skull width W2, it is possible to determine thecentre line of the skull by dividing it by two. When in step 111 thecomputer proportions the signal equivalent to the centre line of theobject (e.g. skull) with the signal representing the location of theimaging object being imaged (e.g. jaw joint), the reference locationdata equivalent to the centre line i.e. the symmetry plane of the skullis obtained. In this way, the reference location data can be scaled intothe same coordinates with the location data of the imaging object.Advantageously, the support point of the object positioning means, e.g.the support element supporting the forehead of the ‘headgear’ or thepossible jaw support, is directed to support the object (the head) atthe point of the above centre line or symmetry plane.

According to an embodiment, reference location data is determined instep 109 by taking an optical image of the object, e.g. the patient, thepatient's head or other part, by a camera being connected to the imagingapparatus and by measuring e.g. a dimension of the patient's head, suchas the skull width, from the optical image, whereby the referencelocation data can be determined based on the dimension measured e.g. ina way described above. Advantageously, said dimension measured or datacalculatable of it is used as the reference location data. As an aid indetermining the reference location data, it is possible to use data onthe distance between the camera and the object or some other equivalentdata based on which it is possible to measure from the optical imagee.g. the width of the patient's head based on which, again, thereference location data can be determined.

According to an embodiment in step 111, based on the reference locationdata of the object and the location data of the imaging object in theimaging area is determined the location of the imaging object inrelation to the reference location data, e.g. the distance of theimaging object from a plane determined by the reference location data.From now on, the imaging object in the imaging area in step 103 and itslocation data are referred to as a first imaging object and locationdata of a first imaging object. The location data of the first object isdetermined as described in step 105 and the reference location datarelated to the first imaging object as described in step 109. In step111, the location data of the first imaging object, e.g. its centre, inrelation to the reference location data is determined, when the patientis positioned such that the first imaging object is positioned in theimaging area, whereby advantageously the support point of the object isfocused to support the object (e.g. the head) such that the objectremains stationary.

According to an example, the support point of the object positioningmeans is focused to support the object at the point of a planedetermined by said reference location data. According to an example, thedistance of the first imaging object from a line or plane determined bythe reference location data is determined by calculating by thecomputer. According to an example, the location data of the firstimaging object can be determined by means of a distance and an anglefrom a line or plane determined by the reference location data bycalculating by the computer.

According to an embodiment in step 113, the location data of a secondimaging object belonging to the object is determined, which secondimaging object is located in relation to the first imaging objectcomparably determined by the reference location data of the object.According to an example, the second imaging object is located at adistance determined by the reference location data in relation to thefirst imaging object. According to an example, the second imaging objectis typically located on the opposite side of a plane determined by thereference location data, e.g. the symmetry plane, in relation to thefirst imaging object when the first imaging object is in the imagingarea. The location data of the second object is obtained e.g. as adistance determined by the reference location data in relation to thelocation data of the first object (displacement according to distance inrelation to said first object). Alternatively, the location data of thesecond object is obtained e.g. rotating the location data of the firstobject in a desired way in relation to the reference location data, e.g.symmetrically onto the opposite side of the symmetry line. The locationdata of the second imaging object can be determined e.g. by projectingthe location data of the first imaging object in relation to a line orplane determined by the reference location data. According to anexample, the location data of the second imaging object is obtained byprojecting the distance of the first imaging object in relation to theline or plane determined by the reference location data on its oppositeside (displacement according to distance in relation to saidline/plane). According to an example, the location data of the secondimaging object is obtained by projecting a position vector describingthe distance and the angle of the location data of the first imagingobject onto its opposite side from a line or plane determined by thereference location data (rotation according to position vector inrelation to said line/plane). Based on the above, it is possible todetermine e.g. the distance between the first and the second imagingobject and/or the distance of the second imaging object from the centreline of the reference location data and/or the angle of the secondimaging object in relation to the centre line of the reference locationdata.

In a way described above in step 113, the location data of the secondimaging object is discovered in relation to the location data and/orreference location data of the first imaging object when the firstimaging object is in the imaging area according to step 103. The supportpoint of the object positioning means is focused to support the object(e.g. the head) such that the object remains stationary, whereby thefirst and the second imaging object are located symmetrically onopposite sides in relation to the reference location data when the firstimaging object is in the imaging area.

According to some embodiments, it is possible to determine the locationdata of the second imaging object determinable in step 113 beforedetermining the location data of the first imaging object occurring instep 105 or simultaneously with determining the location data of thefirst imaging object occurring in step 105. In other words, determiningthe location data of the first and the second imaging object is notbound to occur in any specific order. Then advantageously, in step 109is first determined reference location data which relates to thelocation data of the first and the second imaging object. For instance,the above skull measurement can determine e.g. the skull width as thereference location data, whereby the location data of the first and thesecond imaging object are determined based on the skull width. Then, theskull width determines the distance of the first and the second imagingobject from each other and the location data of the first and the secondimaging object can be determined in a desired order or evensimultaneously.

According to an embodiment in step 115, the imaging area is adjustedbased on the location data of the second imaging object determined instep 113 such that the second imaging object is positioned in theimaging area. The positioning of the second imaging object in theimaging area for imaging is based on, according to an example, thepositioning of the first imaging object in the imaging area (step 103)such that the device generating X-rays and the device detecting X-raysare automatically adjusted in relation to the imaging area, whereby thelocation of the imaging area for imaging the second object is adjustedwith the location data of the first imaging object in relation to thereference data. Then, the imaging area is adjusted based on the locationdata of the first imaging object and said reference location data forimaging the second imaging object belonging to the object, whereby thefirst and the second imaging object are located in a desired way inrelation to the reference location data, e.g. at a desired distance fromeach other or symmetrically in relation to the reference location data.Advantageously in step 115, the object being imaged remains setstationary whereby, when adjusting the imaging area, the first and thesecond imaging object remain stationary. Advantageously in step 115, theobject being imaged remains set stationary such that the objectpositioning means, e.g. the support point of the object positioningmeans, is focused to support the object at a desired point, e.g. at thepoint of a line or plane determined by the reference location data. Instep 115, the device generating X-rays and the device detecting X-raysmove and/or rotate in relation to the object being imaged beingstationary such that the imaging area between the device generatingX-rays and the device detecting X-rays is positioned at the point of thelocation data of the second imaging object determined in step 113. Inother words, in relation to the imaging of the first imaging object instep 115, the imaging area between the device generating X-rays and thedevice detecting X-rays moves and/or rotates for a distance between thefirst and the second imaging object, for a displacement according to theline/plane determined by the reference location data of the distance ofthe first imaging object onto the opposite side of the line/planedetermined by reference location data or in relation to the distance andthe angle of the first imaging object for a displacement/rotationaccording to the line/plane determined by the reference location dataonto the opposite side of said line/plane. There is then no need toposition the second imaging object separately in the imaging area, butthe location of the second object to be imaged is found out based on thelocation data of the first object and the reference location datarelated to it, e.g. a distance or the location of a symmetry line.

Alternatively in step 115, the device generating X-rays and the devicedetecting X-rays rotate in relation to the object being imaged beingstationary such that the imaging area between the device generatingX-rays and the device detecting X-rays is positioned at the point of thelocation data of the second imaging object determined in step 113 bylimiting X-rays by at least one dynamic collimator. When the imagingarea is adjusted by limiting X-rays by at least one dynamic collimator,the device generating X-rays and the device detecting X-rays rotatearound the imaging object being between them in the imaging area suchthat a rotation centre formed by the device generating X-rays and thedevice detecting X-rays does not move during the adjustment of theimaging area and imaging.

Alternatively, the imaging area can be adjusted with a hybrid solutionwhere the imaging area is focused by limiting by at least one dynamiccollimator and by moving the rotation centre formed by the devicegenerating X-rays and the device detecting X-rays during the adjustmentof the imaging area and imaging. Then, the rotation centre moves betweenthe imaging objects for some travel but for a shorter travel than thefull distance of the imaging objects.

In a corresponding way as in step 107 in connection with the imaging ofthe first imaging object, in step 117 the second imaging object isimaged after the second imaging object is in the imaging area accordingto step 115. Advantageously, the imaging area is at the point of thefirst imaging object when an image is taken of it (step 107) and at thepoint of the second imaging object when it is taken (step 117).Advantageously, the first (step 107) and the second imaging object (step117) are imaged at one imaging event.

In step 117, the device generating x-rays and the device detectingX-rays rotate around the imaging object being between them in theimaging area, whereby desired projection images of the imaging objectare taken e.g. on each cycle of 180-360 degrees. A three-dimensionalimage is reconstructed by a computer applicable for image processingfrom projection images taken from different directions of the imagingobject. The completed three-dimensional image consists of 3D pictureelements i.e. voxels. The second imaging object in the imaging area canbe imaged as a whole with a specific number of projection images whichare transferred after imaging to a computer to be reconstructed as athree-dimensional image which can be shown on the display of thecomputer. The computer calculates the projection images e.g. in threedirections being perpendicular against each other, thus forming anintegrated three-dimensional image of the imaging area. Thethree-dimensional processing of the imaging area enables the fact thatthe imaging object can always be shown from an optimal direction.Advantageously, imaging is based on an X-ray beam sent by the devicegenerating X-rays towards the imaging object in the imaging area,whereby the device detecting X-rays receives the X-ray beam havingpenetrated the imaging object. For instance, a suitably pulsed beamforms when rotating around the imaging object with each pulse aprojection image of which the three-dimensional image is calculated forits part. In this way, three-dimensional images are obtained from thefirst and the second imaging area with one positioning, e.g. performedin step 103.

According to an embodiment in step 119, the first projection imagestaken in step 107 being in the X-ray image data format and the secondprojection images taken in step 117 are saved in the X-ray image datafile for further processing. The first projection images taken in step107 can also be saved whenever after step 107 in the X-ray image datafile. Advantageously, the set of projection images is saved in the X-rayimage data file. From the sets of projection images saved in the X-rayimage data file, three-dimensional X-ray images of the imaging objectsare reconstructed by the computer e.g. in ways known in the field. Asthe location data of the first and the second imaging object are boundto each other in the above way e.g. as distances between them or theirdistances and angles in relation to the reference location data, thefirst and the second projection images are saved in the samethree-dimensional coordinates as registered either in separate X-rayimage data files or a common X-ray image data file. Advantageously, thefirst and the second imaging object are imaged during one imaging event,whereby the first and the second projection images are together incommon coordinates.

Each three-dimensional image saved in the X-ray image data file can beprocessed further as a set of cross-sectional images. On a freely chosensection plane, a cross-sectional image is determined of athree-dimensional image, e.g. a cylinder. When the three-dimensionalX-ray image data of the imaging object is presented as one X-ray imagedata file or two single X-ray image data files having commoncoordinates, it is possible to perform measurements between the firstand the second imaging object, e.g. measurements of an angle or adistance from the reference plane/line or measurements of distancebetween the imaging objects. The three-dimensional X-ray image dataformed of the first and the second imaging object can also be presentedas two X-ray image data files such that they have common coordinates,whereby it is possible to show the cross-sectional images of the firstand the second imaging object equivalent to each other at the same timeand simultaneously perform measurements between the X-ray image datafile in three-dimensional coordinates. Each X-ray image data fileconsists of several cross-sectional images, whereby the cross-sectionalimages of the first and the second imaging object corresponding to eachother can be examined in a desired way and measurements performedbetween corresponding cross-sectional images. When the computertomographic images of the first and the second imaging object are in thesame coordinates with the reference location data in the X-ray imagedata files, the first and the second imaging object can then be examinedby means of cross-sectional images determined by freely chosen sectionplanes.

FIG. 2 shows by means of an example the positioning of a left jaw joint211 being in a jaw area 202 to an imaging area 210 which is locatedbetween a device generating X-rays 206 and a device detecting X-rays208. When imaging, the device generating X-rays 206 advantageously sendsa beam 204 towards the left jaw joint 211 in the imaging area 210,whereby the device detecting X-rays 208 receives an X-ray beam 204having penetrated the left jaw joint 211. When imaging, the movements ofthe device generating X-rays 206 and the device detecting them 208 aresynchronised such that an image of the imaging area 210 of a desiredshape can be saved from the device detecting X-rays 208 in a memory.Advantageously, the device generating X-rays 206 and the devicedetecting X-rays 208 rotate on a circular orbit 220 synchronised to eachother around a rotation axis passing via a centre of the imaging area210. Advantageously, the device generating X-rays 206 and the devicedetecting X-rays 208 are attached at the opposite ends of a supportingarm or its parts, which supporting arm or its parts are movably attachedto the frame of the imaging apparatus and rotate around its rotationaxis. For instance when rotating for 180-360°, image data is taken ofthe left jaw joint 211 which consist of projection images taken fromdifferent directions. When a desired number of projection images havebeen taken, a three-dimensional image of the left jaw joint 211 isreconstructed of the projection images by the computer. In FIG. 2, thecentre of the imaging area 210 is depicted by an intersection ofstraight lines 234, 236, 237 being perpendicular against each other. Thestraight line 237 (which is perpendicular against the paper plane)simultaneously depicts the above rotation axis. When the left jaw joint211 is positioned in the imaging area 210, the intersection of thestraight lines 234, 236, 237 detects the location data of the left jawjoint 211 in the imaging area 210. The location data of the left jawjoint 211 is proportioned to the rotation axis (straight line 237) inthis case. For a diameter of the imaging area being imaged 210, in whichthe left jaw joint 211 is imaged, is chosen a desired area around theintersection of the straight lines 234, 236, 237. The left jaw joint 211in the imaging area 210 can be indicated by an indicator means 214 a,216 a, 218 a which shows e.g. the centre of the imaging area 210. Theindicator means comprises one or more indicators 214 a, 216 a, 218 a,e.g. a laser indicator, which indicate the intersection of the straightlines 234, 236, 237 advantageously in their direction. The indicator 218a indicates the centre of the imaging area 210 in the direction of therotation axis (straight line 237) (even though drawn on the side of FIG.2). The imaging apparatus can also comprise at least a second indicatormeans formed of one or more indicators 214 b, 216 b, 218 b, which can,when desired, indicate some other point in the object than the imagingobject e.g. the reference point of the object (e.g. point in thesymmetry plane of the jaw area) in the intersection of the straightlines 232, 238, 239. The straight line 239 (which is perpendicularagainst the paper plane even though drawn on the side of FIG. 2) isparallel with the above rotation axis.

In FIG. 2, the reference location data of the jaw area depicts a planeor a line passing via the intersection formed by the straight lines 232,238, 239 on different sides of which the left and the right jaw joint211, 213 belonging to the jaw area 202 locate symmetrically. Above inconnection with describing step 109 were depicted various ways todetermine the locations of the left jaw joint 211 and the symmetryplane/line in relation to each other and the location of the right jawjoint 213 in relation to the location of the left jaw joint 211 and/orthe location of the symmetry plane/line. When e.g. the symmetry planepassing via the intersection formed by the straight lines 232, 238, 239is used as the reference location data, in FIG. 2 a distance a depictsthe distance between the left jaw joint 211 and the symmetry plane and adistance b the distance between the left and the right jaw joint 211,213, whereby the location data of the right jaw joint 213 can bedetermined based on the above data. For instance, the distance b can beused as the reference location data. When e.g. the symmetry line passingvia the intersection formed by the straight lines 232, 238, 239 is usedas the reference location data, in FIG. 2 by means of distances a and cand an angle w between the straight lines 238 and 243 the location ofthe left jaw joint 211 in relation to the symmetry line can bedetermined, whereby the location data of the right jaw joint 213 can bedetermined based on the above data. According to an embodiment, theobject, e.g. the patient's head being imaged, is supported for keepingit stationary in a desired way or e.g. at a point determined by thereference location data, e.g. in the middle of the jaw, by an objectpositioning means, e.g. a jaw support.

FIG. 3 shows according to an embodiment the adjustment of the imagingarea from a location 210 automatically to a location 210′ when, inaddition of the imaging of the left jaw joint 211 shown in FIG. 2,wishing to image the right jaw joint 213. Then, the positioning of theright jaw joint 213 in the imaging area 210′ is based on the earlierpositioning of the left jaw joint 211 in the imaging area 210 and thedetermining of the location data of the right jaw joint 213 in a waydescribed above. According to an example, the jaw area 202 is supportede.g. by a jaw support or other object positioning means at a desiredpoint or at the point of a symmetry plane/line in order for the jawjoints being imaged remain stationary as precisely as possible duringimaging. According to FIG. 3, the displacement and/or rotation of theimaging area from the location 210 to the location 210′ is determinedbased on the location data of the right jaw joint 213, e.g. based on thedistances a, b and/or c and/or the angle w depicted in FIG. 2. Whenimaging the right jaw joint 213 in the imaging area 210′, a devicegenerating X-rays 206′ and a device detecting X-rays 208′ rotate on acircular orbit 220′ synchronised to each other around a rotation axispassing via the centre of the imaging area 210′. When imaging, thedevice generating X-rays 206′ advantageously sends a beam 204′ towardsthe left jaw joint 213 in the imaging area 210′, whereby the devicedetecting X-rays 208′ receives the X-ray beam 204′ having penetrated theleft jaw joint 213. For instance when rotating on the circular orbit220′ of 180-360°, image data is imaged of the right jaw joint 213 whichconsist of projection images taken from different directions. When adesired number of projection images have been taken, a three-dimensionalimage of the right jaw joint 213 is reconstructed of the projectionimages by the computer. The projection images taken of the left and theright jaw joint 211, 213 are saved in an X-ray image data file andthree-dimensional images are constructed of them by the computer in away described above (step 119) for further processing.

Alternatively according to another embodiment, the adjustment of theimaging area from the location 210 automatically to the location 210′can be arranged by dynamic collimators, whereby the rotation centre ofthe supporting arm connecting the device generating X-rays 206 and thedevice detecting X-rays 208 to each other remains stationary in relationto the frame of the imaging apparatus and rotates around its rotationaxis. Alternatively, the imaging area 210, 210′ can be adjusted with ahybrid solution where the imaging area is focused by limiting by atleast one dynamic collimator and by moving the rotation centre formed bythe device generating X-rays 206 and the device detecting X-rays 208during the adjustment of the imaging area 210, 210′ and imaging. Then,the rotation centre moves between the left jaw joint 211 and the rightjaw joint 231 for some travel but for a shorter travel than the fulldistance b of the imaging objects. Advantageously, the first and thesecond jaw joint 211, 213 are imaged during one imaging event.

FIG. 4 shows a device 400 according to the invention, e.g. a controlunit or device, by means of which it is possible to control limited-areacomputer tomography imaging. The device 400 is advantageously integratedor otherwise connected to the imaging apparatus. The device 400comprises one or more processors 410 or equivalent programmablecontroller circuits for performing commands defined by the user and/orsoftware and for processing data related to them. The device 400comprises one or more external and/or internal memories 420 for savingand storing data, e.g. commands and other information. The device 400comprises an I/O means 430, e.g. a keyboard, a pointer, an indicator orother user interface e.g. in the control panel, for entering commands,data and other information to the device 400 and/or for receiving themfrom the device 400 and a display 440 for displaying the commands, dataand other information to the user. The device 400 comprises e.g. one ormore control softwares 450 in the memory 420 for controlling the imagingapparatus. The control software 450 can also be partially or totallyfirmware-type device software. Furthermore, the device 400 comprises ameans 460 for determining the location data of the first imaging object,a means 470 for determining the reference location data, a means 480 fordetermining the location data of the second imaging object, and a means490 for determining control parameters in order to adjust the imagingarea according to the location data of the first and/or the secondimaging object. Said means 460, 470, 480, 490 operate together with theprocessor 410 and the memory 420 and at least the means 490 alsooperates together with the control software 450. Advantageously, themeans 460 and the means 470 receive information related to location viathe I/O means 430, e.g. indicator means 214 a, 216 a, 218 a and/orindicator means 214 b, 216 b, 218 b shown in FIG. 2. According to analternative, the means 460 and the means 470 receive information relatedto location from the memory 420, where is earlier saved informationrelated to the location of the same imaging object e.g. based on earlierperformed imagings. According to an alternative, the means 470 receivesinformation related to reference location from a camera (not shown inthe figures) being in connection with the imaging apparatus or itsmemory where there is an image taken of the imaging object at a specificdistance, of which it is possible to measure information related to thereference location data, e.g. dimensional data measured of an imagetaken of the object, such as the patient's head. The memory 420 of thedevice 400 can also comprise e.g. software related to storing and/orprocessing X-ray image data.

The control software 450 together with the processor 410 provides thatthe method according to an embodiment of the invention can be performedin the device 400, e.g. a control device or unit.

According to an embodiment of the invention, the device 400 is arrangedto determine the location data of the first imaging object, to determinethe reference location data related to the first imaging object and toadjust the imaging area based on the location data of the first objectbeing imaged and said reference location data for imaging the secondimaging object. According to an example, the device 460 is arranged todetermine the location data of the first imaging object, when the firstimaging object is positioned in the imaging area, the means 470 isarranged to determine the reference location data related to the firstimaging object, the means 480 is arranged to determine based on thelocation data of the first imaging object and said reference locationdata the location data of the second imaging object, and the means 490is arranged to determine control parameters to adjust the imaging areabased on location data of the second imaging object. The means 490provides the control parameters to the control software 450 which isarranged to adjust the imaging area, e.g. by means of the processor 410and/or the memory 420 and/or at least one of the means 460, 470, 480,based on the location data of the first imaging object and saidreference location data for imaging the second imaging object, wherebythe first and the second imaging object are located at a distance fromeach other determined by the reference location data or symmetrically inrelation to the reference location data. The means 490 for adjusting theimaging area according to the location data of the second imaging objectcomprises determining control parameters e.g. for moving the rotationcentre of the supporting arm connecting the device generating X-rays 206and the device detecting X-rays 208 to each other in relation to theframe of the imaging apparatus. The means 490 can alternatively comprisedetermining control parameters e.g. for a motor for moving collimatorsin relation to the rotation centre of the supporting arm connecting thedevice generating X-rays 206 and the device detecting X-rays 208 to eachother such that the rotation centre remains stationary in relation tothe frame of the imaging apparatus. The means 490 can alternativelycomprise determining control parameters e.g. for a motor for moving theobject positioning means in relation to the rotation centre of thesupporting arm connecting the device generating X-rays 206 and thedevice detecting X-rays 208 to each other such that the rotation centreremains stationary in relation to the frame of the imaging apparatus.Advantageously, the first and the second imaging object are imagedduring one imaging event.

According to an embodiment of the invention, the device 400 is arrangedto adjust the imaging area in relation to the reference location datasuch that the first and the second imaging object remain stationary forthe whole imaging event. Advantageously, the object includes the firstand the second imaging object, e.g. the left and right jaw joints 211,213 belonging to the jaw area 202, whereby the object, e.g. the jaw area202, is supported stationary e.g. at the point of a plane/linedetermined by the reference location data, e.g. at the point of asymmetry line passing via an intersection formed by straight lines 232,238, 239.

According to another embodiment of the invention, the device 400 can bearranged to adjust the imaging area in relation to the referencelocation data such that first the first imaging object is in the imagingarea and then the second imaging object moves to the imaging area. Then,the rotation centre of the supporting arm connecting the devicegenerating X-rays 206 and the device detecting X-rays 208 to each otherremains stationary in relation to the frame of the imaging apparatus androtates around its rotation axis in the imaging situation.Advantageously, the first and the second imaging object are imagedduring one imaging event.

According to an embodiment of the invention, the device 400 can bearranged to focus the imaging area by limiting by at least one dynamiccollimator and by moving the rotation centre formed by the devicegenerating X-rays and the device detecting X-rays during the adjustmentof the imaging area and during the imaging event. Then, the rotationcentre moves between the imaging objects for some travel but for ashorter travel than the full distance of the imaging objects.

According to an embodiment of the invention, the device 400 is arrangedto adjust the imaging area in relation to the reference location datasuch that the second imaging object is located symmetrically in relationto the first imaging object at the opposite side of the symmetry plane,symmetry axis or centre line of the object depicting the referencelocation data.

According to an embodiment of the invention, the device 400 is arrangedto adjust the imaging area in relation to the reference location datasuch that its distance and direction in relation to the referencelocation data is assessed or measured based on the location data of thefirst imaging object and the location data of the second imaging objectin relation to the reference location data is determined as a projectionof the distance and direction of the first imaging object.

According to an embodiment of the invention, the device 400 is arrangedto determine the location data of the first imaging object in relationto the reference location data by receiving e.g. by the I/O means 430 anindication indicating the first imaging object or an object located at aspecific distance from it, e.g. light or laser indication or otherpointer, whereby the indication is provided by indicating by someindicator means 214 a, 216 a, 218 a the first imaging object or anobject located at a specific distance from it and/or by indicating bysome indicator means 214 b, 216 b, 218 b the reference location data.

According to an embodiment of the invention, the device 400 is arrangedto receive e.g. from the memory 420 and/or the I/O means 430 data on theearlier imaged first imaging object and the reference location, based onwhich the device 400 determines the location data of the first imagingobject in relation to the reference location data.

According to an embodiment of the invention, the device 400 comprises adisplay 440 which is arranged to display the computer tomographic imagesof the first and the second imaging object as their own single X-rayimage data files or as one X-ray image data file, whereby both imagingobjects are proportioned to the reference location data.

According to an embodiment of the invention, the device 400 comprises amemory 420 which is arranged to save and store the computer tomographicimages of the first and the second imaging object as their own singleX-ray image data files or as one X-ray image data file, whereby bothimaging objects are proportioned to the reference location data. Thememory 420 can comprise for processing X-ray image data one or moreimage processing software which are arranged to process e.g. with theprocessor 410 several projection images and X-ray image data filesconsisting of several projection images. An external or internalcomputer, which comprises one or more image processing softwares forprocessing X-ray image data, advantageously receives X-ray image datafiles consisting of projection images saved in the memory 420 andreconstructs three-dimensional X-ray images of them. Thethree-dimensional images of the first and the second imaging objectcorresponding to each other and cross-sectional images formed of themcan be examined in a desired way by the computer and measurementsperformed between corresponding three-dimensional images. Themeasurements can also be performed with cross-sectional imagescorresponding to each other. The X-ray image data file consists ofprojection images, of which the image processing software stored in thememory 420 and/or the image processing software stored in the memory ofa computer intended for image processing is arranged e.g. to reconstructthree-dimensional X-ray images e.g. for displaying on the display 440.The image processing software is arranged, e.g. by means of theprocessor 410 and/or the memory 420, to perform by means of X-ray imagedata files measurements between the first and the second imaging object.Measurements between the X-ray image data file can be performedsimultaneously as the three-dimensional images and/or cross-sectionalimages of the first and the second imaging object equivalent to eachother are examined.

According to an advantageous embodiment, each X-ray image data fileconsists of several cross-sectional images, whereby in the X-ray imagedata files the computer tomographic images of the first and the secondimaging object are in the same coordinates with the reference locationdata, whereby the first and the second imaging object can be examined bymeans of freely chosen cross-sectional images determined by the sectionlevels.

FIG. 5 shows a system 500 according to the invention by means of whichit is possible to control limited-area computer tomography imaging. Thesystem 500 comprises a control device 520 of the above type includinge.g. a processor or a micro controller, a memory, an I/O means, e.g. acontrol panel, and a display. The control device 520 further comprises acontrol software, a means for determining location data of a firstimaging object, a means for determining reference location data, a meansfor determining location data of a second imaging object, and a meansfor determining control parameters in order to adjust the imaging areaaccording to the location data of the second imaging object. The controldevice 520 including e.g. a processor or a micro controller, where isstored the control software, is advantageously integrated to an imagingapparatus 510. Furthermore, the system 500 comprises an imagingapparatus 510 which is by wire or wirelessly in data communication withthe control device 520. The imaging apparatus 510 comprises the devicegenerating X-rays 206 and the device detecting X-rays 208 which areattached at the opposite ends of the supporting arm or its parts, whichsupporting arm or its part is movably attached to the frame of theimaging apparatus and rotates around its rotation axis. Advantageously,the imaging apparatus 510 comprises an object positioning means, whichis adjustably attached to the frame of the imaging apparatus such thatthe object being imaged, which includes the first and the second imagingobject, can be supported at a desired point or e.g. at the point of thereference location data to a position where the first imaging object isin the imaging area. Advantageously, the object includes the first andthe second imaging object, e.g. the left and right jaw joints 211, 213belonging to the jaw area 202, whereby the jaw support operating as theobject positioning means is arranged to support the jaw area 202 at asuitable point or e.g. at the point of a plane/line determined by thereference location data. The object positioning means can also compriseat least two support elements which are adjustable to support thepatient's head on different sides, whereby the patient's skull width canbe measured as described above in connection with the ‘headgear’.Advantageously, the imaging apparatus 510 comprises indicator means 214a, 216 a, 218 a and/or indicator means 214 b, 216 b, 218 b which areattached to the imaging apparatus 510 and (the indication) shown bywhich is proportioned e.g. to the frame of the imaging apparatus 510and/or the rotation axis of the rotating supporting arm connecting thedevice generating X-rays 206 and the device detecting X-rays 208.Furthermore, the system 500 can comprise an image processing unit 530e.g. for processing X-ray image data and reconstructing asthree-dimensional images as described above.

Advantageously, the imaging apparatus 510 comprises the devicegenerating x-rays 206 and the device detecting X-rays 208 which rotatearound the first imaging object 211 in the imaging area 210, wherebydesired projection images of the first imaging object 211 are taken e.g.on each cycle of 180-360 degrees. The control device 520 determines in away described above the reference location data by the means 470 basedon the location data of the first imaging object 211 determined by themeans 460 and, after that, the location data of the second imagingobject 213 by the means 480. The control device 520 determines in a waydescribed above by the means 490 control parameters for the imagingapparatus 510, whereby the control device 520 adjusts the location ofthe device generating X-rays 206 and the device detecting X-rays 208such that they rotate around the second imaging object 213 in theimaging area 210′, whereby desired projection images of the secondimaging object 211 are taken e.g. on each cycle of 180-360 degrees.Alternatively, the control device 520 adjusts the location ofcollimators limiting X-rays such that the device generating X-rays 206and the device detecting X-rays 208 rotate around the second imagingobject 213 in the imaging area 210′, whereby desired projection imagesof the second imaging object 211 are taken. Advantageously, the firstand the second imaging object 211, 213 are imaged at a singlepositioning of the object to be imaged. Advantageously, the first andthe second imaging object 211, 213 are imaged successively during oneimaging event. When the first and the second imaging object 211, 213 areimaged, the object being imaged remains stationary e.g. by means of theobject positioning means in the imaging apparatus 510. Alternatively,the object being imaged moves such that first the first imaging object211 and then the second imaging object 213 is in the imaging area. Theobject being imaged can be moved by means of the object positioningmeans.

According to an embodiment of the invention, the system 500 is arrangedto determine the location data of the first imaging object, to determinethe reference location data related to the first imaging object and toadjust the imaging area based on the location data of the first objectbeing imaged and said reference location data for imaging the secondimaging object, whereby the first and the second imaging object arelocated at a distance determined by the reference location data fromeach other or symmetrically in relation to the reference location data.

According to an embodiment of the invention, a computer program forcontrolling limited-area computer tomography imaging is arranged toperform at least part of the steps 105, 109, 111, 113, 115 and 119 ofthe method illustrated in FIG. 1, when the computer program (controlsoftware) is run in the device 400. e.g. the control device 520, e.g.the processor or micro controller.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to determine the location dataof the first imaging object, to determine the reference location datarelated to the first imaging object and to adjust the imaging area basedon the location data of the first object being imaged and said referencelocation data for imaging the second imaging object, whereby the firstand the second imaging object are located at a distance determined bythe reference location data from each other or symmetrically in relationto the reference location data.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to adjust the imaging area inrelation to the reference location data such that the first and thesecond imaging object remain stationary for the whole imaging.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to adjust the imaging area inrelation to the reference location data such that the second imagingobject is locate symmetrically in relation to the first imaging objectat the opposite side of the symmetry plane, symmetry axis or centre lineof the object describing the reference location data.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to adjust the imaging area inrelation to the reference location data such that assessing or measuringbased on the location data of the first imaging object its distance anddirection in relation to the reference location data and determining thelocation data of the second imaging object in relation to the referencelocation data as a projection of the distance and direction of the firstimaging object.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to determine the location dataof the first imaging object in relation to the reference location databy receiving an indication indicating the first imaging object or anobject located at a specific distance from it.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to determine the location dataof the first imaging object in relation to the reference location databy receiving data of the earlier imaged first imaging object and thereference location.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to display the computertomographic images of the first and the second imaging object as theirown single X-ray image data files or as one X-ray image data file,whereby both imaging objects are proportioned to the reference locationdata.

According to an embodiment of the invention, the computer programcomprises a code means which is arranged to store the computertomographic images of the first and the second imaging object as theirown single X-ray image data files or as one X-ray image data file,whereby both imaging objects are proportioned to the reference locationdata. Advantageously, each X-ray image data file consists of severalcross-sectional images, whereby the cross-sectional images of the firstand the second imaging object correspond to each other can be examinedin a desired way and measurements performed between correspondingcross-sectional images. Advantageously, the computer program comprises acode means which is arranged to perform measurements between the firstand the second imaging object by means of three-dimensional images ofthe first and the second imaging object constructed of X-ray image datafiles. Advantageously, each X-ray image data file consists of severalcross-sectional images, whereby in the X-ray image data files thecomputer tomographic images of the first and the second imaging objectare in the same coordinates with the reference location data, wherebythe first and the second imaging object can be examined by means offreely chosen cross-sectional images determined by the section levels.

Above were described only some embodiments of the arrangement accordingto the invention. The principle of the invention can naturally be variedwithin the scope defined by the claims e.g. for the part ofimplementation details and utilisation areas.

1-15. (canceled)
 16. A method for controlling limited-area computertomography imaging, comprising: determining a reference location data ofan object to be imaged; obtaining location data of a first imagingobject within the object to be imaged; determining a location of thefirst imaging object based upon the location data of the first imagingobject in relation to the reference location data; computer-tomographyimaging a first imaging area about the first imaging object; determininglocation data of a second imaging object based on the location data ofthe first imaging object and the reference location data;computer-tomography imaging a second imaging area about the secondimaging object.
 17. The method of claim 16 wherein the referencelocation data comprises a center plane of the object to be imaged. 18.The method of claim 17, further comprising: measuring a distance acrossthe object to be imaged; and determining the reference location datafrom the measured distance.
 19. The method of claim 18, furthercomprising: supporting the object to be imaged with an objectpositioning means comprising at least two support elements adapted tosupport opposing sides of the object to be imaged; measuring a distancebetween the at least two support elements, where the distance betweenthe at least two support elements is the distance across the object tobe imaged.
 20. The method of claim 19, wherein the object to be imagedis a head of a patient and further the at least two support elementsfurther comprise at least one support element adapted to engage at leastone of a jaw and a back of the head of the patient and at least onesupport element adapted to engage at least one of a forehead or a crownof the head of the patient, the method comprising: determining at leastone of a height and a depth of the head of the patient by measuring adistance between the support elements; determining the referencelocation data as a plane through the head of the patient.
 21. The methodof claim 18, further comprising: capturing an optical image of theobject to be imaged with a camera, wherein measuring the distance acrossthe object to be imaged comprise measuring a distance across the opticalimage of the object to be imaged.
 22. The method of claim 21, furthercomprising: acquiring a distance between the camera and the object to beimaged; and determining the reference location data further based uponthe acquired distance between the camera and the object to be imaged.23. The method of claim 16, wherein the location data of the firstimaging object defines a center of the first imaging object.
 24. Themethod of claim 23, wherein the location data of the first imagingobject is a distance and an angle from a point defined by the referencelocation data.
 25. The method of claim 2416, wherein the referencelocation data defines a plane of symmetry of the object to be imaged andthe location data of the second imaging object is a mirrorrepresentation of the location data of the first imaging object acrossthe plane of symmetry of the object to be imaged.
 26. The method ofclaim 16, further comprising: supporting the object to be imaged with anobject positioning means comprising at least one support element adaptedto engage the object to be imaged such that the object remainsstationary relative to the reference location data.
 27. The method ofclaim 16, further comprising: positioning an x-ray emitter and an x-raycollector about a rotation axis; rotating the x-ray emitter and thex-ray collector about the rotation axis to computer-tomography image thefirst imaging area; and dynamically collimating an x-ray beam producedby the x-ray emitter to computer-tomography image the second imagingarea.
 28. The method of claim 16, further comprising: positioning anx-ray emitter and an x-ray collector at about a rotation axis; duringcomputer-tomography imaging to computer-tomography image both the firstimaging object and the second imaging object: rotating the x-ray emitterand the x-ray collector about the rotation axis; and dynamicallycollimating an x-ray beam produced by the x-ray emitter tocomputer-tomography image the first imaging object and the secondimaging object.
 29. The method of claim 28, wherein the referencelocation data comprises a center plane of the object to be imaged andthe rotation axis is centered on the center plane.
 30. The method ofclaim 28, wherein the reference location data comprises a center planeof the object to be imaged and the rotation axis is located on a side ofthe center plane towards the first imaging object, the method furthercomprising: while rotating the x-ray emitter and the x-ray collectorabout the rotation axis, moving the rotation axis in a direction acrossthe center plane of the object to be imaged towards the second imagingobject.
 31. A system for limited-area computer tomography imaging, theapparatus comprising: an x-ray emitter configured to produce a beam ofx-rays; an x-ray collector configured to receive x-rays having passedthrough an object to be imaged; and a control apparatus communicativelyconnected to the x-ray emitter and the x-ray collector, the controlapparatus determines a reference location of the object to be imaged,obtains location data of a first imaging object within the object to beimaged, determines a location of the first imaging object based upon thelocation data of the first imaging object in relation to the referencelocation data, operates the x-ray emitter and the x-ray collector tocomputer-tomography image a first imaging area about the first imagingobject, determines location data of a second imaging object based on thelocation data of the first imaging object and the reference locationdata, and operates the x-ray emitter and the x-ray collector tocomputer-tomography image a second imaging area about the second imagingobject.
 32. The system of claim 31, further comprising at least twosupport elements configured to engage the object to be imaged, whereinthe at least two support elements support the object to be imaged duringcomputer-tomography imaging of the first imaging object and the secondimaging object.
 33. The system of claim 32, wherein the controlapparatus acquires a position of the at least two support elements anddetermines the reference location as a center plane through the objectto be imaged based upon the acquired position of the at least twosupport elements.
 34. The system of claim 31, further comprising acamera that acquires an optical image of the object to be imaged andprovides the optical image to the control apparatus, and the controlapparatus determines the reference location as a center plane throughthe object to be imaged based upon the optical image.
 35. The system ofclaim 31, wherein the x-ray emitter further comprises a dynamiccollimator and the control apparatus operates the x-ray emitter and thex-ray collector to rotate about a rotation axis while collimating anx-ray beam produced by the x-ray emitter with the dynamic collimator tocomputer tomography image the first imaging area and the second imagingarea.